The present invention relates to a toroidal continuously variable transmission (toroidal CVT) for a vehicle.
A toroidal CVT of a traction-drive type has been proposed and in practical use. Japanese Patent Publication No. (Heisei) 6-72653 discloses a half-toroidal CVT which is designed so as to suppress a spin loss.
However, a torodial CVT generally increases its power loss due to the increase of a spin loss when operated at a low-speed side transmission ratio and a high-speed side transmission ratio. Accordingly, when a vehicle employing the toroidal CVT travels an urban road where the low-speed side transmission ratio range is frequently used and a high-way where the high-speed side transmission ratio range is frequently used, it is difficult to maximally ensure a superior characteristic of the toroidal CVT. This will avoid the vehicle with the toroidal CVT from performing superior energy consumption and superior power performance in such transmission ratio ranges.
It is therefore an object of the present invention to provide a toroidal CVT which is capable of decreasing a total power loss in a low-speed side transmission-ratio range and at a high-speed side transmission-ratio range.
A toroidal CVT according to the present invention comprises an input disc and an output disc coaxial with the input disc. The output disc is disposed opposite to the input disc. A loading cam applies a pressing force proportional to an input torque to the input disc. A power roller is disposed on opposite surfaces of the input and output disc so as to be able to transmit power from the input disc to the output disc. A power-roller supporting member supports the power roller so that the power roller is inclinable on a center of a circular arc of the opposite surface of the input and output discs to vary a ratio between a rotation speed of the input disc and a rotation speed of the output disc within a transmission ratio range. A power-roller bearing is disposed between the power roller and the power-roller supporting member so that the power roller is rotatably supported to the power-roller supporting member. A spin generated at each of a first contact point between the input disc and the power roller and a second contact point between the output disc and the power roller takes positive value throughout the transmission ratio range.